Gene carrier's doctor thus seen in shiny coat (10)
I believe the answer is:
chromosome
'gene carrier's' is the definition.
(I've seen this in another clue)
'doctor thus seen in shiny coat' is the wordplay.
'doctor' becomes 'mo' (medical officer).
'thus' becomes 'so' (synonyms).
'seen in' means one lot of letters goes inside another.
'shiny coat' becomes 'chrome' (I can't justify this - if you can you should believe this answer much more).
'mo'+'so'='moso'
'moso' placed inside 'chrome' is 'CHROMOSOME'.
Can you help me to learn more?
(Other definitions for chromosome that I've seen before include "this could be X or Y" , "Structure carrying genes" , "Gene carrier" , "Genetic structure" , "structure in cell" .)